1. Field of the Invention
The present invention relates to an auxiliary contact unit for a magnetic contactor, and more particularly, to an auxiliary contact unit securely attachable to a magnetic contactor.
2. Description of the Conventional Art
Generally, a magnetic contactor is connected to a wire connected to a system, and opens and closes a circuit on the system. An auxiliary contact unit is used along with the magnetic contactor and functions to open and close a weak current or a low level current employed for, for example, a control signal.
The auxiliary contact unit is typically attachable to a lateral surface or an upper surface of the magnetic contactor, and a certain magnetic contactor has a built-in auxiliary contact unit. A movable unit of an auxiliary contact unit is attached to a magnetic contactor and at the same time is connected to a movable unit of the magnetic contactor to open and close a contact point of the auxiliary contact unit in response to opening/closing operation of the magnetic contactor, and to turn on and turn off the current flowing in the auxiliary contact unit.
One of the methods of attaching an auxiliary contact unit to a magnetic contactor is a snap-fit connection method, but, in order to obtain a secure attachment, a screw or a bolt/nut are used. Regardless of the attachment methods, an auxiliary contact unit must be securely attached to a magnetic contactor in order to withstand or absorb vibrations and shocks that might be involved with opening and closing of the magnetic contactor.
Hereunder, configuration of the conventional auxiliary contact unit, and an attachment method of an auxiliary contact unit to a magnetic contactor will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view illustrating a magnetic contactor attached with an auxiliary contact unit according to prior art. FIG. 2 is a schematic diagram illustrating an auxiliary contact unit according to the prior art, and FIG. 3 is a perspective view illustrating a conventional magnetic contactor.
Referring to FIG. 1, a magnetic contactor (10) is attached at one side thereof with an auxiliary contact unit (20), where the auxiliary contact unit is attached across a part of an upper frame and a lower frame of the magnetic contactor. At this time, the auxiliary contact unit (20) is equipped with a plurality of hooks and lugs at an attachment frame thereof to which the magnetic contactor (10) is attached, as shown in FIG. 2.
In other words, a frame of the auxiliary contact unit (20) is lengthwise provided at an upper surface thereof with a cross-bar lug insertion groove (22) from which a cross-bar lug (21) of the auxiliary contact unit (20) is protruded for vertical movement, and the cross-bar lug insertion groove (22) is formed at left and right sides thereof with upper hooks (23). Furthermore, the frame of the auxiliary contact unit (20) is provided at left and right lower surfaces thereof with fixed lugs (25) and further down there are formed with lower hooks (27).
Referring now to FIG. 3, the magnetic contactor (10) is formed with grooves at positions corresponding to the plurality of hooks and lugs provided at the auxiliary contact unit (20). In other words, upper hook insertion grooves (13) into which the cross-bar insertion groove (11) and the upper hooks (23) are inserted are formed at an upper frame of the magnetic contactor (10), while fixed lug insertion grooves (15) into which the fixed lugs (25) of the auxiliary contact unit (20) are inserted, and lower hook insertion grooves (17) into which the lower hooks (27) are inserted, are formed at a lower frame of the magnetic contactor (10).
Accordingly, the auxiliary contact unit (20) can be attached to the magnetic contactor (10) by inserting the cross-bar lug (21) inserted into an interior of the auxiliary contact unit (20) into the cross-bar lug insertion groove (11) of the magnetic contactor (10), and inserting the upper hooks (23), the fixed lugs (25) and the lower hooks (27) into the upper hook insertion grooves (13), the fixed lug insertion grooves (15) and the lower hook insertion grooves (17) respectively.
At this time, the auxiliary contact unit (20) can be easily attached to the magnetic contactor (10) by the elastic force of a compression spring disposed at a lower inside thereof, the detailed explanation of which will be given with reference to FIGS. 4a and 4b. 
FIG. 4a is a lower horizontal cross-sectional view of an auxiliary contact unit according to prior art, FIG. 4b is a schematic view of a spring cover and a lower hook applied to an auxiliary contact unit according to the prior art and FIG. 4c is a schematic view in which the spring cover of FIG. 4a is removed.
Throughout the drawings, elements, parts or portions similar to or corresponding to those in FIG. 1 to FIG. 3 are designated by like reference numerals.
As illustrated in the drawings, the lower hooks (27) are connected to a cover (28), and the cover (28) is installed thereunder with a compression spring (29). The auxiliary contact unit (20) can be easily attached to the magnetic contactor (10) by inserting the lower hooks (27) of the auxiliary contact unit (20) to the lower hook insertion grooves (17) of the magnetic contactor (10) and using the elastic force of the cover (28) and the compression spring (29).
However, the conventional auxiliary contact unit attachable according to the above method suffers from a number of shortcomings that make it inefficient, for example but not limited thereto, in retaining attachment force thereof.
In other words, although the compression spring facilitates the attachment of the auxiliary contact unit to the magnetic contactor, and serves to support an auxiliary contact and protects the auxiliary contact against shocks or vibrations caused by continued ON/OFF operations of the magnetic contactor, the elastic force of the compression spring comes to deteriorate as time passes and the ON/OFF operations continue, thereby weakening the support strong enough to retain the attachment force of the auxiliary contact unit.